/**
 * CURL SSRF Example
 *
 * @author Feei <wufeifei@wufeifei.com>
 * @link   http://wufeifei.com/ssrf
 */
function callback($callback_url){  
    $ch = curl_init();
    curl_setopt($ch, CURLOPT_URL, $callback_url);
    curl_setopt($ch, CURLOPT_HEADER, 0);
    /*
     * 搜索区块(S规则触发位置之下)中是否存在下面这行配置
     * 存在则不会有风险，反之亦然
     */
    curl_setopt($ch, CURLOPT_PROTOCOLS, CURLPROTO_HTTP | CURLPROTO_HTTPS);  

    curl_exec($ch);
    curl_close($ch);
}